| Co3O4 powder has extensive applications in the fields of catalysis, magnetic material and electro-chemistry. More and more strict specifications are needed for Co3O4 powder in market. According to Co3O4 powder production process of hydro-chemistry method, it is of great signification to develop the right method and theory to control the particle morphology, size and size distribution for preparing high quality Co3O4 powder.In this paper, the basic change laws of the morphology, size and size distribution of the dispersed Co3O4 powder were studied by precipitation in diluent and concentrated solutions of cobalt salt system. The new control method and theory were developed.In diluent cobalt solution, the stages of nucleation and growth were easily divided by homogeneous precipitation process just as what described as La Mer model. In this study, an electrical conductivity detect was applied on line to record the change of the solution electrical conductivity during the reaction and aging. It was found that at the early period of the precipitation the solution electrical conduction rose slowly to a certain extent and then a sudden drop happened following with the gradual restore to a lower but smoother value. It could be determined that the sudden drop was due to the ion concentration decrease quickly because of the burst nucleation. The growth stages could be defined to be the following course of the smooth electrical conductivity. The change of the solution conductivity could be taken as a sign to discriminate the nucleation and growth stages. According to the change of the solution conductivity, it could be determined whether it was needed to finish. reaction or change corresponding conditions, and the mono-disperse powders with definite size were obtained during the experiment.In the homogeneous precipitation system, under the condition of the different reagents concentration, the precipitation particles with diverse morphologies were obtained. The main reason was that the primary particles had different chemical compositions for the effects of the different kinds of anions and stoichio-chemical compositions of the primary particles. The chemical formula of particles was confirmed. TheyABSTRACTare CoIun(OH)o.83(CO3)o.49 Ay 0.14H2O(in tightly-capped reactor: A stands for NO3\ SO42" or Cl"; y[A] moiecuiar weight 12.9) and Co"jnmoiecuiar weight (OH)0.83(NCO)xAy 0. 14H2O. (in open reactor A stands for: NO3\ SO42" or Cl'; 42x+ yCA]?weigh44.82). By replacing CO32" partly in the primary particles by the anions (SO42\ NO3\ Cl") and influencing the chemical polar positions and degrees, the growth kinetics were changed, which led to the formation of particles with different morphologies. The effect degree of the anions depended on the co-existing anion radius in the reaction solution, and their effects on the particles could be showed as S042>C1>N03-.In concentrated solution of cobalt salt precipitation system, the effects of reagents of ammonia carbonate and ammonium oxalate was studied respectively. In concentrated solution, the main mechanism of the particle growth was aggregation. The control of morphology and size was realized by means of controlling the aggregation process. According to the Gibbs Law, the early-formed fine particles had the ability of absorbing molecules or ions in the solution to decrease the interface energy of the precipitation system, which gave an idea of by designing a lower interface tension system to make the particles exist in the thermo-dynamic stable state and produce the mono-disperse system with special morphology and size. The surface of particles was charged by adsorption effect and so the electric barriers against the aggregation between particles were established. The adjusting of surface charging of the particles could be performed by the reference of the zeta potential of the particles in the suspension. The experimental results showed that the zeta potential could be taken as a sign to guide the designing of this kind of stable system. According...
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